DC micro grid solar power philosophy ( as advocated by living energy farms)
I think this is a robust way to design for power use. My only complaint re living energy farms is their complete lack of aesthetics, but as far as living off only DC power solar power, they are well versed and experienced.
It is very efficient in use of material, cost, reliability and years of service you can expect.
Basically, they look at the homes basic needs and subdivided, they call this using DC micro grids.
For example, there are some high power users on a farm like theirs with a shop, power saws, metal working and cutting, a large grain grinder, a well pump, these all take alot of power, but they can be used in the daytime only, easily, so that no storage of power is needed for those uses. They have found that most shop tools can run on straight DC from the panels, even if they used to be run AC ( if they have a universal motor) and that they do not mind a range of amps/volts.
They took stock of what they need to be able to do at night, and concluded that they only need lights at night, and there are a few other things that people might want at night, a fan for summer cooling, charging a device they forgot to charge during the day. A different household might want to run a laptop or other low power device to watch a movie, etc... So, once that list is thought about, not very much battery storage is needed. Batteries are normally very expensive, but if you only need a very small amount of storage, it becomes affordable. They also advocate, and sell, Edson Nickel-Iron batteries, which last an extremely long time, maybe a lifetime, and take alot of abuse and keep working. A disadvantage of those batteries, for me, was that most I had seen made were so large, but if you do not need much storage, they have small, easy to carry or move ones that living energy farms sells.
For their household, they have a third circuit that has no battery storage, and that powers a DC refrigerator directly, a charging station for phones/laptops, and a fan for their solar thermal air house heating system. They call this and the shop/well circuit "daylight drive solar" things that are only running when the sun is out.
Another nice thing about a distributed system is that it can be added to later if there is money. They just did a volunteer set up in the desert southwest on a couple of reservations of basic solar/battery systems that were to only provide light and phone charging. This is such a life changer for people there who do not have grid electricity or running water, to not have to fire up a generator just to have light or the phone, or not have to go to town and buy kerosene or candles. This type of very small cabin set up they sell for a few hundred dollars, and includes everything, DC LED light bulbs, 10 amp hours edison batteries, a mini flashlight, a table lamp, a cigerette socket for charging a small device. They just installed 47 small lighting systems just last month, here is a bunch of photos of installs/happy reciepients http://livingenergyfarm.org/solar-installations-2020/
"....DC Microgrids are effective because they work with the strengths of renewable energy, rather than trying to use it to replace fossil fuels as a bulk commodity. The emphasis is on designing systems to meet specific energy needs. For this reason we like to describe the DC Microgrid as a permaculture approach to energy systems.
A DC Microgrids looks different for each site, depending on wind and solar resources, local climate and energy needs, etc. But the design principles remain the same everywhere. These principles are:
1. Maximize conservation, efficiency and insulation. Solar energy is only useful when demand is minimized.
2. Minimize battery size by storing energy in forms other than electricity. The bulk of the stored energy in a DC Microgrid takes forms such as a hot or cold thermal mass, pressurized water, or bio-gas.
3. Operate high-demand electrical appliances as daylight drive only. In daylight drive systems, DC (direct current) motors and resistive loads are wired directly to photovoltaic panels with no batteries or other hardware involved. These appliances are used only during the day.
4. Keep electrical hardware as simple and durable as possible. A DC Microgrid side steps inverters and AC (alternating current) electricity, and uses nickel iron batteries, a non-toxic technology that lasts 40 years or more.
I could see something that is a small, new build, like Dave T's office and granny unit, powered inexpensively by this type of thing, leaving the laundry area, maybe freezer, on the main house circuit. So, then the small granny unit and separate office are also a good backup, a place with at least the basics, lights, charging, DC refrigerator maybe, if AC power goes out to the main house circuits.